Treatment of landfill gas

ABSTRACT

The present invention relates to a method of abating hydrogen sulfide gas emitted by or generated in landfills. Certain embodiments of the present invention relate to contacting hydrogen sulfide gas with Fuller&#39;s earth or other carrier materials and metals such as silver, copper, iron, zinc or mixtures thereof, and other components.

This application claims priority to U.S. Provisional Patent ApplicationNo. 60/512,327 filed Oct. 17, 2003 under 35 U.S.C. §119(e) and U.S.Non-provisional patent application Ser. No. 10,799,434 filed on Mar. 11,2004 under 35 U.S.C. §120.

BACKGROUND OF INVENTION

The invention relates to the abatement of toxic and/or noxious gases,particularly the abatement of hydrogen sulfide gas emitted by orgenerated in landfills.

Hydrogen sulfide is a flammable, poisonous gas with a characteristicoffensive odor of rotten eggs. In high concentrations, H₂S can beextremely hazardous. At concentrations of greater than about 500 ppm,hydrogen sulfide can be fatal to humans.

Hydrogen sulfide gas can be released by various sources such as coalpits, gas wells, sulfur springs and decaying organic matter. Hydrogensulfide generated by decaying organic matter is generally the product ofanaerobic digestion, and can be released by solid waste landfills,sewage treatment facilities, paper mill waste, cattle feed lots, poultryfarms, and other industries employing anaerobic digestion forprocessing. Anaerobic digestion takes place in the absence of oxygenresulting in the formation of methane (CH₄), ammonia (NH₃), hydrogensulfide (H₂S) and phosphine (PH₃).

Landfills are sometimes located within close proximity to residentialareas. Such close proximity creates the potential of exposure tohazardous conditions such as gas emissions. As such, there exists a needto abate toxic and offensive gases such as hydrogen sulfide gas that aregenerated.

SUMMARY OF INVENTION

The present invention relates to a method of abating hydrogen sulfidegas emitted by landfills and other sources. Certain embodiments of thepresent invention relate to contacting hydrogen sulfide gas with metalssuch as silver, copper, iron, zinc or mixtures and salts thereof, andother components, which can be combined with carrier materials, such asFuller's earth (described below). One embodiment of the inventionrelates to the use of Fuller's earth, AgNO₃, Fe₂(SO₄)₃ or other metalcompounds of general formula Me_(x)(SO_(y))_(y) or Me_(x)(NO₃)_(y),alone or mixed with carrier material, applied in and/or over a landfilland/or mixed with fill prior to its deposit on a landfill. In oneembodiment of the invention, the hydrogen sulfide abating material isadded in layers.

It is advantageous to combine these and other metal containing materialswith carrier materials, such as Fuller's earth, clay, diatomaceousearth, zeolite material, activated charcoal, alumina, silica, aluminumsilicate, magnesium aluminum silicate, magnesium silicate and otherporous or high surface area materials. This can increase surface contactbetween the hydrogen sulfide gas and the metals and provide otherbenefits, such as improving reaction kinetics. Combinations of the metalcontaining materials with Fuller's earth are particularly preferred. Thecombinations discussed above, of carrier or porous materials, with anamount of aforementioned metal containing materials, increases theremoval efficiency for hydrogen sulfide gas than the use of eithercomponent alone.

Fuller's Earth is a naturally occurring sedimentary clay composed mainlyof alumina, silica, iron oxides, lime, magnesia and water in variableproportions. As used herein, it also includes magnesium silicates andaluminum silicates having similar properties. Other types of claymaterials that could be used are ball clay, bentonite, fire clay andkaolin to name a few.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the several steps and the relationof one or more of such steps with respect to each of the others, and thecomposition of matter embodying features of construction, combination(s)of elements and arrangement of parts which are adapted to effect suchsteps, all as exemplified in the following detailed disclosure, and thescope of the invention will be indicated in the claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It has been determined that hydrogen sulfide gas emitted by or generatedin landfills may be treated with a mixture of components to abate itsoffensive odors and neutralize its toxicity to surrounding communities.Abatement of the hydrogen sulfide gas is such that the gas is emitted ata concentration less than 10 ppb.

In one embodiment of the invention, hydrogen sulfide gas, mercaptan andsulfur components are abated with silver nitrate and/or silver nitratesolution. This is preferably combined with Fuller's earth, magnesiumaluminum silicate, aluminum silicate or magnesium silicate, andcombinations thereof; plus, optionally, any of eucalyptus, benzaldehydeand citronella. Other carrier materials as identified above are alsouseful.

In another embodiment of the invention, hydrogen sulfide gas is abatedwith ferric sulfate and/or ferric sulfate solution. This is preferablycombined with Fuller's earth, magnesium aluminum silicate, aluminumsilicate or magnesium silicate, and combinations thereof; plus, any ofbenzaldehyde and citronella.

In another embodiment of the invention, hydrogen sulfide gas is abatedwith copper sulfate and/or copper sulfate solution. This is preferablycombined with Fuller's earth, magnesium aluminum silicate, aluminumsilicate or magnesium silicate, and combinations thereof; plus any ofbenzaldehyde and citronella.

In another embodiment of the invention, hydrogen sulfide gas is abatedwith a solution of silver nitrate and/or a solution of zinc sulfate.This is preferably combined with Fuller's earth, magnesium aluminumsilicate, aluminum silicate or magnesium silicate, and combinationsthereof; plus any of benzaldehyde and citronella.

In yet another embodiment of the invention, hydrogen sulfide gas isabated with a solution of silver nitrate and/or a solution of zincsulfate. This is preferably combined with Fuller's earth, magnesiumaluminum silicate, aluminum silicate or magnesium silicate, andcombinations thereof.

The amount of metals such as silver, copper, iron, zinc or mixtures andsalts thereof, used in the present invention are typically in the rangefrom about 1 ppm to about 5,000 ppm, preferably in the range from about10 ppm to about 500 ppm, with the remainder as a carrier, preferably asilicate carrier and other additives. The silicate carrier is preferablyincluded in the range from about 70% wt. to about 85% wt.

Compositions for abating landfill gas can be represented by, but are notlimited to, the following examples, which are not intended to beconstrued as limiting.

EXAMPLE 1

Component Amount Fuller's Earth 85% Fragrance 1-2% Benzaldehyde 1-4%Citronella 0.25% Water 11-13% Silver Nitrate 300 ppm

EXAMPLE 2

Component Amount Fuller's Earth 74% Eucalyptus 80/85 2% Lemon PK-970.45% Citronella 0.10% Water 10-15% Silver Nitrate 300 ppm

EXAMPLE 3

Component Amount Fuller's Earth 85% Cherry Fragrance 2% Benzaldehyde 4%Citronella 0.25% Water 10-15% Zinc Sulfate 2,500-3,000 ppm SilverNitrate 100 ppm

EXAMPLE 4

Component Amount Fuller's Earth 80% Water 10-20% Zinc Sulfate 2,500 ppmSilver Nitrate 100 ppm

EXAMPLE 5

Component Amount Fuller's Earth 80% Water 15-20% Ferric Sulfate2,500-5,000 ppm Cherry Fragrance 2% Benzaldehyde 2-4% Citronella 0.25%

EXAMPLE 6

H₂S Abatement

Tests were performed using 195 grams of the composition of Example 3 totreat various combinations of H₂S concentration and flow rate. Hydrogensulfide gas was prepared at selected concentrations in a gas bag and waspumped through a column reactor at a controlled flow rate using aperistaltic pump. The effluent gas was passed through an absorbingsolution trap (impingers) where hydrogen sulfide was absorbed byalkaline cadmium hydroxide solution. The absorbed sulfide wassubsequently determined by spectrophotometric measurement of themethylene blue produced from sulfide in a color development procedure.The hydrogen sulfide determination procedure was based on the methodprovided in “Methods of Air Sampling and Analysis” by James P. Loage,incorporated herein by reference. Out method detection limit was 10 ppb.

Experimental results are presented in Table 1. The test was conductedunder dry conditions. TABLE 1 Experimental Results of 1st Column ReactorTest Feed Flow H₂S Mass H₂S Conc. in Cumulative H₂S Conc. Feed Vol. RateLoading Cumulative H₂S Mass Loading H₂S Mass in Effluent Mass RemovedRun (ppm) (Liter) (L/min) (μg) Mass loaded (μg) Rate (μg/min) Effluent(μg) (ppm) by Column (μg) 1 10 30 0.78 420 420 11 ND ND 420 2 10 30 0.78420 840 11 ND ND 840 3 50 30 0.78 2,100 2,940 55 ND ND 2,940 4 50 300.46 2,100 5,040 32 ND ND 5,040 5 100 30 0.46 4,200 9,240 64 ND ND 9,2406 100 30 0.78 4,200 13,440 109 ND ND 13,440 7 250 20 0.46 7,000 20,440161 ND ND 20,440 8 500 20 0.46 14,000 34,440 322 4 0.15 34,436 9 500 300.78 21,000 55,440 546 423 10.08 55,017 10 100 20 0.78 2,800 58,240 10915 0.54 58,225 11 500 30 0.78 21,000 79,240 546 2,160 51.43 77,080 12500 20 0.46 14,000 93,240 322 420 14.99 92,820 13 500 30 0.78 21,000114,240 546 2,226 53.01 112,014 14 500 20 0.46 14,000 128,240 322 41114.68 127,829 15 500 10 0.28 7,000 135,240 196 470 33.56 134,770 16 10020 0.46 2,800 138,040 64 90 3.20 137,950

The results showed that the column could remove hydrogen sulfide tobelow detection limit of 10 ppb for at least 20 mg of hydrogen sulfide.After a cumulative mass loading of 34.4 mg of hydrogen sulfide (test run#8), level above the reported odor threshold (i.e. 5 to 10 ppb) in theeffluent was suspected.

After test run #8, the column's performance in hydrogen sulfide removalseemed to depend on the mass loading rate (μg/min). Test run #9 with ahigh mass loading rate of 546 μg/min resulted in 10 ppm of effluentconcentration which is the NIOSH exposure limit. However, test run #10with a lower mass loading rate of 109 μg/min resulted in a much lowereffluent concentration (0.54 ppm). It should be noted that 0.54 ppm isstill above the odor threshold.

It was observed that the column can effectively control hydrogen sulfideat a dosage rate between 20 mg to 34 mg H₂S per 195 gram of compositionused. This translates to 0.1 to 0.17 mg H₂S/g of composition. Suitablecompositions in accordance with the invention are able to eliminate over0.01 mg H₂S, preferably 0.05 mg H₂S per gram of composition.

Application methods for using the compositions include, but are notlimited to, a layering approach and a mixing approach. In the layeringapproach, a layer of any combination of the compositions in the Examplesis applied onto the surface of a landfill. To ensure adequateperformance, the layer has a minimum thickness of 2 cm. Layer thicknessmay vary based on H₂S concentrations at different landfills. In themixing approach, any combination of the compositions in the Examples ismixed with landfill material and applied to the surface of a landfill.

Compositions for abating landfill gas are advantageously made by mixingFuller's earth with a metal compound. Upon mixing, the Fuller's earth iscoated with the metal compound to form a uniform granular mixture. Theapproximate average granular size of the mixture is advantageously inthe range from about 1 mm to about 8 mm in diameter, preferably fromabout 3 mm to about 6 mm in diameter. Larger particle sizes can lessonthe amount of dust created in application. The uniform granular mixtureadvantageously has a specific gravity from about 0.70 to about 0.85.

Using a minimum average thickness of 2 cm and using, as a basis, alandfill with a surface area of 250 acres, the composition in the layerof mixture to be applied at a landfill can comprise from about 65 toabout 75 tons of composition per acre of landfill. The metalconcentration in the layer is advantageously from about 0.1 tons toabout 2.5 tons of metal in per acre of landfill.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in carrying out the above method andin the constructions set forth without departing from the spirit andscope of the invention, it is intended that all matter contained in theabove description and shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

It is understood to be that the following claims are intended to coverall of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which, as amatter of language, might be said to fall there between.

Particularly, it is understood that in said claims, compounds recited inthe singular are intended to include compatible mixtures of suchcompounds wherever the sense permits.

1. A composition for abating hydrogen sulfide emissions comprising: acombination of a metal compound of the general formulaMe_(x)(SO_(y))_(y) or Me_(x)(NO₃)_(y) and a carrier metal compound,formulated to eliminate at least 0.01 grams of H₂S per gram ofcomposition.
 2. The composition of claim 1 wherein the metal compoundcomprises Fuller's earth.
 3. The composition of claim 1 furthercomprising a fragrance, a benzaldehyde, citronella, eucalyptus andwater.
 4. The composition of claim 1, wherein the carrier metal compoundis silver nitrate or silver nitrate solution.
 5. The composition ofclaim 1, wherein the carrier metal compound is ferric sulfate or ferricsulfate solution.
 6. The composition of claim 1, wherein the carriermetal compound is copper sulfate or copper sulfate solution.
 7. Thecomposition of claim 1, wherein the carrier metal compound is a mixtureof silver nitrate and zinc sulfate solutions.
 8. The composition ofclaim 2, wherein the Fuller's earth is comprised of magnesium silicate,aluminum silicate or combinations thereof.
 9. The composition of claim1, wherein the carrier metal compound is present in the composition inan amount from about 1 ppm to about 5,000 ppm.
 10. The composition ofclaim 2, wherein the Fuller's earth is present in an amount from about70% wt. to about 85% wt.
 11. The composition of claim 3, wherein thefragrance is present in an amount from about 1% wt. to about 2% wt. 12.The composition of claim 3, wherein the benzaldehyde is present in anamount from about 1% wt. to 4% wt.
 13. A method of reducing landfillgas, comprising mixing a composition formed by combining a metalcompound of the general formula Me_(x)(SO_(y))_(y) or Me_(x)(NO₃)_(y)and a carrier medtal compound formulated to eliminate at least 0.01grams of H₂S per gram of composition with landfill material and applyingthe mixture to the surface of a landfill.
 14. A method of reducinglandfill gas, comprising applying a layer of a composition formed bycombining a metal compound of the general formula Me_(x)(SO_(y))_(y) orMe_(x)(NO₃)_(y) and a carrier metal compound formulated to eliminate atleast 0.01 grams of H₂S per gram of composition on the surface of alandfill, wherein said layer has a minimum average thickness of 2 cm.15. The method of claim 14, wherein the layer comprises at least about65 tons of the composition per acre of landfill.
 16. The method of claim14, wherein the layer comprises from about 65 tons to 75 tons of thecomposition per acre of landfill.